This invention relates to a signal generating mechanism for producing an electrical signal in the form of a pulsating DC voltage. The signal has a frequency proportional to the angular velocity of a rotating shaft and may have a duty cycle which is a fixed percentage of the period of the pulsating DC electrical signal. The signal generating mechanism is particularly suitable for use in a distributor of a breakerless ignition system for a multi-cylinder internal combustion engine.
Common past practice in ignition systems for multicylinder internal combustion engines has been to employ a set of breaker points in a distributor to generate sparks as required by the engine. Recently, these breaker points have been replaced by breakerless ignition systems that employ alternating current signal generating mechanisms, such as the signal generating mechanism shown in U.S. Pat. No. 3,783,314 issued Jan. 1, 1974 in the name of Charles C. Kostan and assigned to the assignee of the present invention. These alternating current signal generating mechanisms determine the times or instants at which the breakerless ignition system generates sparks in the various engine combustion chambers. Although signal generating mechanisms of this type produce an alternating voltage signal having a frequency proportional to the angular velocity of a rotating shaft, the voltage signal has an amplitude that is proportional to the angular velocity. This is disadvantageous at low angular velocities.
It has been proposed in the prior art that a Hall effect magnetic sensor be utilized to generate an electrical signal having a frequency proportional to the angular velocity of a rotating shaft. U.S. Pat. No. 3,875,920 issued Apr. 8, 1975 to Marshall Williams describes a signal generating mechanism of this kind used in the ignition system for an internal combustion engine. The signal generating mechanism described in this patent includes a stator having a C-shaped permanent magnet structure with a Hall effect sensor positioned between the north and south poles of the permanent magnet structure. A rotor has depending vanes which, when in alignment with the poles of the permanent magnet structure, shunt the magnetic field thereof and reduce the magnetic field in the Hall effect sensor. A similar structure is illustrated in U.S. Pat. No. 3,861,370 issued Jan. 21, 1975 to H. E. Howard.